ci: remove Claude Code workflow (auto-PR-review + @claude responder) (#470)

Deletes .github/workflows/claude-review.yml entirely. This workflow
auto-ran Claude on every pull_request (opened/synchronize/reopened)
and also responded to @claude mentions in issues/PR comments. Both
are removed — no Claude automation runs on the repo after this.

PR review going forward is handled by Gemini Code Assist (tagged
per-PR per the team convention).

Co-authored-by: Ignacio Van Droogenbroeck <ignacio@vandroogenbroeck.net>

Author: xe-nvdk